Waste vegetable oil was co-liquefied with swine manure to determine the bio-oil potential in this study. The result shows that co-liquefaction of waste vegetable oil with swine manure can improve the bio-oil production and decarboxylation of waste vegetable oil. The weight ratio of swine manure to waste vegetable oil exerted a great effect on both the yield and quality of the bio-oil. The optimum weight ratio of swine manure to waste cooking oil was 1: 3, where a maximum oil yield of 80% was obtained with higher calorific value up to 38 MJ/kg.